It is a goal in steam turbine power generation to increase power output and decrease corrosion in the exhaust hood and condenser of a power generating unit. One method of doing this is by measuring and controlling electric charge released to steam from the turbine and the various charge release regions within the exhaust hood near to the turbine as described in U.S. Pat. No. 5,992,152 by Weres.
If the amount of negative charge in the steam is large enough to produce intense electrical discharge activity, severe corrosion of carbon steel structural members and turbulence is created, which in turn decreases the power output of the generating unit. Therefore, corrosion may be controlled and power output increased by blocking the release of negative charge, such as by a small net positive charge added to the steam. However, excessive values of positive charge in the steam also have similar deleterious effects.
The amount of electric charge in the steam is a function of the amount of ammonia or another volatile base added to the feedwater. A system of automatic control which controls ammonia feed rate in response to measured charge is used to maintain charge density at a predetermined set-point which provides increased power output and decreased corrosion.
In the prior art, control probes collect the current from the control probe to ground proportional to charge density at the specific location of that probe. Correlating values of the current from the probes to ground indicate the minimum value of the current from the probe to ground needed to make the space charge throughout most of the exhaust hood and condenser positive.
Control probes, however, are an added complexity to an already complicated system. They are subject to malfunction, corrosion and by their nature need to be placed in the exhaust path, adding to turbulence. What is needed is a system for monitoring and controlling charge in the turbine exhaust moisture without use of the invasive and fragile control probes. This will increase the reliability of steam turbine power generation systems, and even increase their efficiency. Other difficulties with the prior art also exist, some of which will be apparent upon further reading.